This invention relates to a stator coil structure for a rotating field electrical machine and a method of manufacturing the same and more particularly to an improved coil structure and method of forming it that will provide high efficiency and compact size.
Most rotating electrical machine are comprised of relatively rotatable rotors and stators. One of the rotor and stator carries a plurality of spaced permanent magnets that cooperate with electrical coil windings formed on the other of these members. It is the formation of the electrical coil windings that determines in large part the efficiency of these types of machines. Generally, the winding mechanisms and methods previously proposed have been something less than totally efficient and have at times resulted in very expensive methods and resulting products. This can be best explained by a description of the various types of structures and methods that have been employed for the coil windings. Generally there have been five methods of winding the coils.
The first method may be characterized as a xe2x80x9cdirect windingxe2x80x9d method wherein a transverse oscillating system is provided and a winding in the form of an enameled wire is wound around the magnet pole tooth of the core using a needle through which the winding is passed. The winding is wound adjacent the magnetic pole tooth and two upper and lower winding guides slide alternatively between the poles to deposit the windings on them. Alternatively the needle is reciprocated in the slot between the pole teeth and directly winds the wire onto the teeth.
The disadvantage with this type of winding method is that the needle for winding the wire must be placed into the slot from the open end thereof and or the guides must move into this area requiring a dead space between adjacent windings. This restricts the winding density and lowers the space factor thereof. Even when winding guides called formers are employed, the winding lacks alignment and it is difficult to increase the winding density. It is also difficult to apply this method to a stator having a large number of magnetic pole teeth or a revolving field type coil having a small inside diameter. Furthermore, the winding device is complicated in structure and becomes quite large.
When winding guides (formers) are used the resulting rubbing contact with the wire can strip or damage the insulating enamel coating and decrease the electrical efficiency.
In connection with an inner rotor type a stator core is divided into radially protruding portions with a continuous inner periphery and an outer peripheral core is fitted thereon. One way in which this type of device is made is that a coil is wound around a bobbin on the protruded portions. Then the outer peripheral core is fitted after the coil winding. This is called a bobbin winding method.
Another way the inner rotor type is made, is that the windings are wound directly on a core having radially protruding sections with an insulating material interposed there between. Then the outer peripheral core is fitted thereon. This is called an outer winding method.
The disadvantages with this second type of construction is that the divided core must be fitted together so that dimensional accuracy is maintained and also to prevent subsequent separation of the parts. Also, the coils must be prevented from bulging out to the outer periphery of the device. This results in complexity in the structure and low production efficiency.
With the bobbin winding method, the winding may deform the bonding flanges and the winding density cannot be enhanced. In addition interference with the outer peripheral core and the dead spaces at the flanges thereof prevent the winding density from being enhanced. In this case, there are deficiencies of lowering the space factor as with the first mentioned method.
A third type of winding method uses divided pole cores. In this case, the armatures are formed as segments, each having a respective pole tooth. Each pole tooth is wound and then the individual segments are fixed together in a suitable manner, normally by welding using a laser beam. This method is not only expensive but raises problems in connection with the dimensional accuracy and the costs involved with the extra steps.
A further method employs what is called a xe2x80x9csawingxe2x80x9d method. In this case, a solid core is employed having a plurality of teeth. A needle is passed sequentially through the slots between the magnetic pole teeth in a back and forth sawing motion to wind the winding. This method has the same disadvantages as the first method step described. Also high stresses are placed on the wire that can result in breakage or rupturing of the insulation.
Another method is the so-called xe2x80x9carmadilloxe2x80x9d type method. In this case, the core is formed in a circular shape and then deformed into a linear shape as used with a linear motor. The winding is then placed on the cores and then the device is again joined by welding the previously cut ends. Again, this method has problems of dimensional accuracy and also because of the stresses exerted on the windings during the successive curving operation, reliability is considerably decreased.
Another type of mechanism for winding employs a needle that is held outside of the slot between the armature teeth at one end of the core and a cam shaped member is provided for reciprocating the winding onto the core. These methods also have considerable disadvantages. In this type of mechanism, the holding and releasing mechanism for the winding is very complicated and the winding action must be repeated during each turn so that rapid productivity is not possible. In addition, the repetition of holding and releasing does not insure good alignment. Even though the needle never enters the slots, a mechanism for introducing the windings into the slots is needed. When this is done, the insulation on the windings may be disturbed.
Thus, the conventional rotating machine presents a problem in that the stator should having windings of a large diameter to permit low voltage and large current to obtain high power. In addition, a large number of magnetic pole teeth are desirable to reduce cogging and to provide smoother rotation and better efficiency. This again results in difficulties in forming the winding.
It is, therefore, a principal object to this invention to provide an improved winding arrangement and coil assembly for a rotating machine wherein accurate coils can be formed having a high density with minimum gaps between the coil windings of adjacent pole teeth.
It is also an object to the invention to provide a method and apparatus wherein the efficiency of such a machine can be significantly improved.
My aforenoted co-pending application discloses a number of embodiments that achieve these objects. However there is still a possibility of obtaining of further advantages. With all of the embodiments therein tapered insert pieces are employed for guiding the Wire toward the opposite end of the pole from the needle. The height of the end of the tapered insert pieces in the area of the needle limits the number of possible windings in this area. Thus maximum winding density is somewhat compromised.
It therefore is a principle object of this invention to provide insert pieces that achieve the objects of my aforenoted application and which offer the possibility of even greater winding density.
Another area of possible improvement lies in the area of the looping projections employed in my earlier application. This adds to the cost of the construction and increases the length of the wiring. The latter disadvantage in addition to adding to the cost increases the electrical resistance. This reduces the efficiency of the machine.
It is therefore a still further object of this invention to provide a construction that achieve the objects of my aforenoted application without requiring loop over projections for the cross over wires.
A first feature of this invention is adapted to be embodied in a rotating electrical machine that comprises a stator having a circular core of a magnetic material and a plurality of magnetic pole teeth extending radially from the circular core. A rotor is juxtaposed to the terminal ends of the magnetic pole teeth and spaced from the circular core. Each of the magnetic pole teeth defines a core and an enlargement at the terminal end of the core. The adjacent pole teeth define slots having a mouth formed between adjacent enlargements. An insulator covers the cores of the magnetic pole teeth. Coil windings are wound around the cores of the magnetic pole teeth with the insulator being interposed there between. Each of the insulators has a circumferential length that decreases in an axial direction along their length.
A method of winding the coils of a rotating electrical machine forms another feature of the invention. In this method, a circular core of magnetic material with a plurality of magnetic pole teeth extending radially from the circular core is provided. Each of the magnetic pole teeth defines a core and slots formed there between. Each of the slots defines a mouth that is formed between adjacent outer ends of the cores. The winding method comprises the steps of positioning a threading needle having an opening through which the wire for the winding of the coils is fed into proximity to one of the mouths. The needle opening is moved in a path around one of the pole teeth and at one side of the slot without moving the needle in any substantial distance along the length of the one pole tooth to form a first winding. The movement of the needle opening is continued in a path around the one of the pole teeth at the one side of the slot without moving the needle in any substantial distance along the length of the one pole tooth to form succeeding windings. The circumferential length of the pole teeth decreases in an axial direction along their length and the wire end is held at the end of the pole tooth spaced from the needle so that each successive winding forces the previous winding along the pole tooth toward the circular core without requiring movement of the needle in any substantial distance along the length of the one pole tooth so that the needle not be moved any substantial distance into the slot.